1. Field of the Invention
The invention relates to a secondary air supply system which supplies air into exhaust gas in an internal combustion engine, and a secondary air supply method of the same.
2. Description of the Related Art
There is a conventional internal combustion engine including a secondary air supply mechanism which supplies secondary air to an exhaust gas control catalyst using an electric air pump, as disclosed in Japanese Patent Laid-Open Publication No. 8-128320.
Also, there is a technology in which control of an air-fuel ratio is performed considering an amount of adsorption material in a catalyst, as disclosed in Japanese Patent Laid-Open Publication No. 9-72235. In addition, there is a technology in which a delay in control of secondary air is corrected, as disclosed in Japanese Patent Laid-Open Publication No. 63-179119.
The exhaust gas control catalyst is in an excessive oxygen state, i.e., in a state where an amount of oxygen is excessive, immediately after the secondary air supply mechanism is stopped. Therefore, if a vehicle is accelerated thereafter, it becomes difficult for the catalyst to purify NOx. Also, immediately after the secondary air supply mechanism is started, for example, much time may be required to increase the rotational speed of an air pump, and a supply amount of the secondary air may become insufficient. Thus, when a fuel amount is increased at the time of the secondary air supply, oxygen may become insufficient, and accordingly the exhaust emission may deteriorate.